The present invention relates to illuminators and image displays.
There is broadly known a projector adapted to illuminate a light modulator by an illuminator and project, with magnification, the image light exiting from the light modulator onto a screen through use of a projection system, such as a projection lens.
The illuminator of such a projector, conventionally, uses a metal halide lamp, a halogen lamp or the like. Recently, the use of a semiconductor laser (LD) is proposed in an effort to reduce the size of the illuminator and hence of the projector. The laser light source has advantages including well color reproducibility, capability of displaying a video image with brightness and contrast, and capability of instantaneous switching, besides the reduction in size.
However, because laser light is coherent, a speckle pattern with a random distribution of light and dark points arises in the video light projected with magnification. The speckle pattern is caused by the interference in irregular phase relationship of between those of light exiting from various points of the projection system. The video image having such a speckle pattern is problematic because of inflicting a flashy flicker feeling upon an observer.
In order to overcome the problem, JP-A-6-208089 discloses a display that, by vibrating/rotating a diffusion element due to an external force, a speckle pattern is changed in a time shorter than a rewrite time of display perceivable by the human so that the observer at his/her eyes is free from catching the speckle through the averaging based on integration effects.
However, the art of JP-A-6-208089 requires a mechanical driver, such as a motor, to vibrate/rotate the diffusion element, thus increasing the device size and the cost thereof. In addition, it costly requires a diffusion element durable against an external force because an external force is applied from the driver to the diffusion element. Furthermore, with a simple reciprocal motion, a pattern integration effect decreases because of once stoppage, resulting in a speckle pattern perception even if making an averaging. Incidentally, speckle becomes less susceptible to perceive as vibration/rotation speed of the diffusion element increases. However, there is a difficulty in vibrating the diffusion element of the device at high speed because it has a significant size. In addition, if mechanically vibrated, noise problematically arises.